Rotating well blowout preventers are constructed to seal about the rotating Kelly joint or the drill pipe during a well drilling operation to prevent blow outs caused by the escape of well fluids under high pressures.
Drillers employ rotating heads primarily for drilling with mud whose density cannot supply sufficient hydrostatic head to balance the pressure of fluids contained in pores of exposed formations. In such operations, both gas and liquids flow continuously into the well bore. The rotating head enables the driller to impose back pressure at the head so as to control the bottom hole pressure and, in consequence, the rate of inflow. It also permits him to trip the pipe under pressure. Low density mud costs less to buy and less to pump. Low bottom hole pressure increases bit life and penetration rate.
There are many prior rotating blowout preventers in the art but for various reasons, such prior devices have not performed totally satisfactorily. Among the reasons for their poor performance is the inability to contain the higher pressures encountered during the drilling operation. This failure to resist the higher pressures is caused by reason of the drive bushing and the sealing element which engage the Kelly joint not being properly arranged to fully accommodate the usual lateral movement of the Kelly occurring between the rotary table and the blowout preventer stack. This results in excessive loads and wear being imposed not only upon the sealing element but also upon the Kelly joint. Further, the prior art has not recognized the importance of the shape and specific construction and reinforcement of the sealing element to maintain a proper seal about the rotating Kelly joint or pipe.
Another reason for inadequate performance has been an excessive wear upon or early failure of the bearings which support the rotating parts. This is the result of inadequate or improper location and mounting of the bearings relative to the position of the sealing element and the rotating housing of the unit. And lastly, although the prior art suggests that the sealing assembly should be capable of being latched and unlatched from the remainder of the structure by remotely controlled means, no satisfactory or efficient way of performing such latching and unlatching has been developed.